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Full text of "Handbook Of Chemical Engineering - I"

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POWER GENERATION AND TRANSMISSION                  41
the usual range of costs for preparation. This may be compared with the losses incident to gasifying the coal in a producer plant, due regard being paid to the folio wing factors:
1.  The costs of coals suitable for gasifying and pulverizing may differ.
2.  Pulverizing equipment and gasifying equipment involve different initial costs.
3.  Gas produced from coal may be used either as a boiler fuel or direct, in the cylinder of a gas engine.
Briquetting involves a cost of $1 to $2 per ton over that of raw fuel.
Wood.—Solid wood fuel prepared for the purpose, is occasionally used under boilers in the Northwest. Split fir at $3 per cord, delivered, is about equivalent economically to the local low-grade coals at $2.20 per ton. Refuse wood fuels (slab, edgings, chips and sawdust) are more frequently employed. Suitable methods of feeding must be provided: fine particles may be blown long distances. If the moisture content is large, a special furnace on the Dutch oven principle may be found necessary. Woods contain very little ash.
STEAM-PLANT PIPING
Materials.—Pipe may be wrought (welded soft steel), cast-iron, brass, galvanized wrought, galvanized sheet riveted. Wrought pipe is standard ("full") weight, extra strong or double extra strong. Inside sizes are nominal up to 13 in., above which size pipe is purchased by the actual external diameter and the standard thickness is % in. The heavier pipes are of the same external diameter and threading. Cast-iron pipe is made with either flanged or bell and spigot joints, the latter being used underground with lead and oakum calking. Classes A to H (A. W. W. Association, U. S. Cast Iron Pipe & Foundry Co.) describe various weights of the latter, increasing from those suitable for 100 ft. head to weights recommended for 800 ft. head. Common "soil pipe" should not be used. Standard lengths are 12 ft.: sizes from 3 to 84 in. Flanged end pipe is obtainable in the same classifications and weights, sizes ranging from 3 to 48 in. Brass pipe should be specified as "iron pipe size." It will then match cast-iron fittings and threads, and will be sufficiently rugged. Galvanized wrought pipe is used in the smaller sizes only. Galvanized sheet riveted pipe may be employed for low pressures and large diameters. The spirally-riveted form is the stronger.
Joints.—Common screwed joints may be used up to 2>£ in., with ground joint unions for the smaller and flange unions for the larger sizes. Screwed joints are more readily made tight but add to the difficulty of alteration or replacement. "Making up" by machine is usually desirable for sizes above 2 in. Flanged joints offer much variety. The commonest form runs the flange up on the thread while the pipe end is still back of the flange face. The tongued and grooved flange decreases the area of flange bearing and therefore increases the unit contact pressure due to bolt tension. This joint may if desired be formed by the pipe ends themselves. Eiveted and peened joints are rightfully obsolete. The best plain flange joint is made by running the pipe clean through the flange (without shouldering on the thread) and facing off on centers. In the various modifications of the Van Stone joint, a very soft pipe is used, this is slipped through the flange without threading and the pipe end is flanged over and faced off so that there is no possibility of a thread leak. Welded flanges are